Islamabad , Pakistan -LRB- CNN -RRB- -- Attackers in Pakistan have hit another convoy carrying fuel for NATO troops in Afghanistan , killing one person , authorities said .

The attack , which occurred Monday , was the fourth attack in as many days on convoys carrying fuel to support the NATO forces .

Gunmen fired on a convoy of oil tankers in the Kalat district of Pakistan 's western Balochistan province , said Bashir Ahmed , a police official in Kalat . One person died , police said .

Attackers struck two convoys on Friday and a third on Sunday .

The Pakistani Taliban has claimed responsibility for two of those attacks , a central spokesman for the militant group told CNN by telephone Monday .

One of the attacks took place Friday against a convoy of NATO supplies near Shikarpur in the southern Sindh province . The other took place Sunday in the capital of Islamabad , killing three local guards .

Azam Tariq , the Pakistani Taliban spokesman , said both the recent attacks on NATO supply efforts were carried out as revenge for drone strikes and NATO 's attacks in Pakistan .

`` U.S. and NATO forces are killing innocent Pakistanis , which is unacceptable , and we will teach them a lesson by such attacks , '' Tariq said .

On Monday , Islamabad police said four people were arrested in connection with the Sunday attack , which also left eight drivers injured .

A convoy was attacked in Baluchistan on Friday , killing a driver and his aide . The Taliban has not claimed responsibility for that attack .

The convoys are operated by contracting Pakistani logistics firms , using local trucks and drivers .

The Pakistani Taliban said a special squad has been appointed to hit U.S. interests in Pakistan , especially NATO supply efforts .

`` The special squad is fully capable to cut off the route for NATO supplies by carrying attacks on the trucks , '' Tariq said .

`` I give final warning to the drivers and the owners of the trucks to stop working for NATO , otherwise our squad will make them exemplary , '' Tariq said .

Pakistan halted NATO supply convoys from entering Afghanistan Thursday after officials blamed cross-border NATO helicopter fire for the deaths of three Pakistani soldiers .

The troops were killed when three NATO helicopters crossed from Afghanistan into Pakistani airspace early Thursday and attacked a military outpost , the government said .

On Monday , NATO 's secretary general said an investigation has been launched into the incident .

`` I expressed my regret for the incident last week in which Pakistani soldiers lost their lives , and my condolences to the families . Obviously , it was unintended . Obviously , we have to make sure we improve coordination between our militaries and our Pakistani partners , '' NATO Secretary General Anders Fogh Rasmussen said .

Pentagon spokesman Geoff Morrell said he expects findings of a NATO probe into the Pakistan incident to be released Wednesday night .

Morrell also said the U.S. military is hopeful that the closed supply route from Pakistan to Afghanistan will be opened `` as soon as possible , '' but the closure has not affected the ability to supply NATO troops .

`` We are making progress on that front , '' Morrell said at a news conference on Tuesday , in reference to talking to Pakistan 's government about reopening the Torkham gate .

Morrell said that the fuel convoy attacks by the Taliban have affected about 1 percent of the supplies that move from Pakistan to Afghanistan .

The route is most important for fuel transport but said even if the gate remained closed for a while , the ability to supply fuel to troops in Afghanistan would not be affected , he said .

Journalists Nasir Habib , Nasir Dawar and Laura Perez Maestro contributed to this report .

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Attack on convoys carrying fuel for NATO troops was fourth in four days

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One person was killed in the attack Monday , police said

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The Pakistani Taliban has claimed responsibility for two earlier convoy attacks

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Pakistani Taliban : `` U.S. and NATO forces are killing innocent Pakistanis ''